The IP (Internet Protocol) Multimedia Subsystem (IMS) is a standardized architecture for providing both mobile and fixed multimedia services that many telephony service providers are beginning to implement. The IMS architecture can include a collection of different functions (i.e., network elements) that communicate using standard protocols.
A user of an IMS network using a mobile device or any user equipment (UE) may place an emergency call, such as a 911 call (in North America) or a 112 call (in most of Europe). Such calls are typically handled by a Public Safety Answering Point (PSAP), which might coordinate an appropriate response to the emergency. After an emergency call is terminated, the PSAP may place a call back to the user for various reasons. For example, if the emergency call appears to have terminated abnormally, the PSAP might call the user back to determine if the user wishes to convey any additional information. Alternatively, the PSAP might call the user back to ask for information that was inadvertently not requested in the initial call. Other reasons for a call back from a PSAP to an emergency caller after the termination of an emergency call may be familiar to one of skill in the art.